Effect of pravastatin, a potent 3-hydroxy-3-methylglutaryl-coenzyme A reductase inhibitor, on survival of AH130 hepatoma-bearing rats

Rho GTPases in hepatocellular carcinoma

Rho GTPases are major regulators of signal transduction pathways and play key roles in processes including actin dynamics, cell cycle progression, cell survival and gene expression, whose deregulation may lead to tumorigenesis. A growing number of in vitro and in vivo studies using tumor-derived cell lines, primary tumors and animal cancer models strongly suggest that altered Rho GTPase signaling plays an important role in the initiation as well as in the progression of hepatocellular carcinoma (HCC), one of the deadliest human cancers in the world. These alterations can occur at the level of the GTPases themselves or of one of their regulators or effectors. The participation into the tumorigenic process can occur either through the over-expression of one of these components which presents an oncogenic activity as illustrated with RhoA and C or through the attenuation of the expression of a component presenting tumor suppressor activity as for Cdc42 or the RhoGAP, DLC-1. Consequently, these observations reflect the heterogeneity and the complexity of liver carcinogenesis. Recently, pharmacological approaches targeting Rho GTPase signaling have been used in HCC-derived models with relative success but remain to be validated in more physiologically relevant systems. Therefore, therapeutic approaches targeting Rho GTPase signaling may provide a novel alternative for anti-HCC therapy.

Pravastatin reduces lung metastasis of rat hepatocellular carcinoma via a coordinated decrease of MMP expression and activity

BACKGROUND/AIMS

Statins have beneficial effects in early pre-clinical models of hepatocellular carcinoma (HCC). Our aim was to test the efficacy of pravastatin on the progression of established HCC in rat, and to study its mechanisms.

METHODS

HCC was induced with diethylnitrosamine and N-nitrosomorpholine. After 14 weeks, all rats developed HCC and then received pravastatin or its solvent for 10 weeks (10 rats/group).

RESULTS

Liver tumor mass was lower in pravastatin group (PG) than control group (CG), as estimated from the number of liver tumors (p<0.004) and the liver weight/body weight ratio (p<0.04). Every CG rat surviving at 24 weeks (4/4) had lung metastasis, against only 5/8 in PG. Moreover, the percentage of lung surface occupied by metastasis was 10-fold smaller in PG than CG (p<0.016). Pravastatin decreased liver matrix metalloproteinase (MMP)-9 activity and mostly suppressed MMP-2 activation (p<0.004), likely because it decreased expression of MMP-14 and tissue inhibitor of matrix metalloproteinases-2 (p<0.01), required for MMP-2 activation.

CONCLUSIONS

Pravastatin reduces progression and limits metastatic diffusion of established HCC. This could be linked to the decreased MMP activity. These results, obtained in a very aggressive HCC model, further suggest the potential benefit of statins in human HCC.

HMG-CoA reductase inhibitors and the malignant cell: the statin family of drugs as triggers of tumor-specific apoptosis

The statin family of drugs target HMG-CoA reductase, the rate-limiting enzyme of the mevalonate pathway, and have been used successfully in the treatment of hypercholesterolemia for the past 15 years. Experimental evidence suggests this key biochemical pathway holds an important role in the carcinogenic process. Moreover, statin administration in vivo can provide an oncoprotective effect. Indeed, in vitro studies have shown the statins can trigger cells of certain tumor types, such as acute myelogenous leukemia, to undergo apoptosis in a sensitive and specific manner. Mechanistic studies show bcl-2 expression is down-regulated in transformed cells undergoing apoptosis in response to statin exposure. In addition, the apoptotic response is in part due to the depletion of the downstream product geranylgeranyl pyrophosphate, but not farnesyl pyrophosphate or other products of the mevalonate pathway including cholesterol. Clinically, preliminary phase I clinical trials have shown the achievable plasma concentration corresponds to the dose range that can trigger apoptosis of tumor types in vitro. Moreover, little toxicity was evident in vivo even at high concentrations. Clearly, additional clinical trials are warranted to further assess the safety and efficacy of statins as novel and immediately available anti-cancer agents. In this article, the experimental evidence supporting a role for the statin family of drugs to this new application will be reviewed.

Effect of simvastatin alone and in combination with cytosine arabinoside on the proliferation of myeloid leukemia cell lines

BACKGROUND

Cholesterol biosynthesis is regulated by the activity of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase. Cholesterol and its derivatives are required in high concentrations by neoplastic proliferating cells for both DNA synthesis and cell growth. Thus, inhibition of HMG-CoA reductase could effect cell cycle progression and proliferation. Therefore, we examined the effect of an HMG-CoA reductase inhibitor (simvastatin) alone and in combination with cytosine arabinoside (ARA-C) on the proliferation of two AML cell lines.

METHODS

AML blasts derived from two cell lines (HL-60 and AML-2) were incubated with increasing concentrations of either simvastatin alone or simvastatin alone for 24 hours with ARA-C added thereafter. The effect of the drugs on cell proliferation in liquid culture (3H thymidine uptake) and on clonogenic assay was analyzed.

RESULTS

We found that the number of proliferating AML blasts (suspension cultures) and colony formations (agar cultures) of both cell lines declined significantly after incubation with simvastatin. Preincubation of both cell lines with simvastatin by the addition of increasing concentrations of ARA-C produced a degree of growth inhibition that was significantly greater than that of the individual compounds. This antigrowth interaction was additive rather than synergistic.

CONCLUSIONS

We conclude that simvastatin has a major antiproliferative effect on AML blasts in vitro. Also, the combination of simvastatin and ARA-C significantly enhanced the antiproliferative effect of each drug. These findings may open new avenues in both the laboratory and clinical research of the treatment of leukemia.

Dose-dependent effects of lovastatin on cell cycle progression. Distinct requirement of cholesterol and non-sterol mevalonate derivatives

The mevalonate pathway is tightly linked to cell proliferation. The aim of the present study is to determine the relationship between the inhibition of this pathway by lovastatin and the cell cycle. HL-60 and MOLT-4 human cell lines were cultured in a cholesterol-free medium and treated with increasing concentrations of lovastatin, and their effects on cell proliferation and the cell cycle were analyzed. Lovastatin was much more efficient in inhibiting cholesterol biosynthesis than protein prenylation. As a result of this, lovastatin blocked cell proliferation at any concentration used, but its effects on cell cycle distribution varied. At relatively low lovastatin concentrations (less than 10 microM), cells accumulated preferentially in G(2) phase, an effect which was both prevented and reversed by low-density lipoprotein cholesterol. At higher concentrations (50 microM), the cell cycle was also arrested at G(1) phase. In cells treated with lovastatin, those arrested at G(1) progressed through S upon mevalonate provision, whereas cholesterol supply allowed cells arrested at G(2) to traverse M phase. These results demonstrate the distinct roles of mevalonate, or its non-sterol derivatives, and cholesterol in cell cycle progression, both being required for normal cell cycling.

Inhibitory effect of simvastatin on the proliferation of human myeloid leukaemia cells in severe combined immunodeficient (SCID) mice

SCID mice were inoculated intravenously with cells from the human HL60 myeloblastic leukaemia cell line and then treated with the 3-hydroxy-3-methylglutaryl coenzyme A (HMG CoA) reductase inhibitor, simvastatin, by subcutaneous continuous infusion. The effect of the drug was measured by subsequent colony formation of surviving HL60 cells in vitro and flow cytometry. The number of clonogenic HL60 cells was reduced in the bone marrow of mice that received simvastatin compared with control mice by 65% and 68% in two separate experiments. The number of clonogenic, normal, murine, bone marrow progenitor cells concomitantly exposed to simvastatin in vivo, was not affected in either experiment. Flow cytometric analysis of bone marrow and spleen cells confirmed these results by showing that simvastatin had reduced the percentage of human leukaemia cells in these tissues by 70% and 88% respectively. The data show that the reported selective effect of simvastatin against acute myeloid leukaemia cells in vitro, can be extended to this in vivo model. HL60 bears an N-ras mutation. In further in vitro studies, ketoconazole, an inhibitor of cholesterol biosynthesis post farnesyl pyrophosphate synthesis, had a similar effect to simvastatin on HL60 colony development. Furthermore, the clonogenicity of a population of N-ras mutated, primary acute myeloid leukaemia (AML) cells was no more sensitive to simvastatin than a population without the mutation. The data suggest that the inhibition of AML cell proliferation by simvastatin may be independent of the RAS signalling pathway.

Suppression by pravastatin, an inhibitor of p21ras isoprenylation, of hepatocarcinogenesis induced by N-nitrosomorpholine in Sprague-Dawley rats

The effect of pravastatin, an inhibitor of p21ras isoprenylation, on hepatocarcinogenesis induced by N-nitrosomorpholine and on p21ras isoprenylation were investigated in male Sprague-Dawley rats. Rats received i.p. injections of pravastatin (10 and 20 mg kg(-1) body weight) every other day and, from the beginning of the experiment, were given drinking water containing N-nitrosomorpholine for 8 weeks. Visible white nodules and hepatic lesions staining positively for gamma-glutamyl transpeptidase or glutathione-S-transferase, placental type, were examined macroscopically or histochemically. In week 15, pravastatin at both dosages significantly reduced the incidence, number and volume of visible white nodules. Quantitative histological analysis also showed that prolonged administration of pravastatin at both dosages resulted in significant reductions in the number and percentage area of hepatic lesions positive for gamma-glutamyl transpeptidase and glutathione-S-transferase, placental type. Administration of pravastatin also significantly decreased the amount of membrane-associated p21ras in the tumour and the labelling index of neoplastic nodules and increased the apoptoic indices of neoplastic nodules. These findings indicate that pravastatin suppresses hepatocarcinogenesis and suggest that this effect might be related to pravastatin's inhibition of p21ras isoprenylation and its subsequent inhibition of cell proliferation and induction of apoptosis in neoplastic lesions.

Chemopreventive efficacy of low dose of pravastatin, an HMG-CoA reductase inhibitor, on 1,2-dimethylhydrazine-induced colon carcinogenesis in ICR mice

Potential chemopreventive action of de-escalated doses of pravastatin (Pr), an HMG-CoA reductase inhibitor, on 1,2-dimethylhydrazine.2HCl (DMH)-induced colon tumorigenesis was evaluated in ICR mice. Thirty mice each in 4 groups received an intraperitoneal injection of 20 mg DMH/kg body weight once weekly for 10 weeks, and were given drinking water dissolved Pr at the concentration of 10 ppm, 5 ppm, or 0 ppm (control) throughout the experiment. The incidence of colon tumors examined at week 35 was significantly lower in the Pr-treated groups than the control group: 20%. 21% and 23% vs. 55%. However, the tumor multiplicity/tumor-bearing animal was increased in the Pr-treated groups compared to the control group. Of all the tumors, 66 were adenocarcinomas in the distal colon and 5 were squamous cell carcinomas at the anus. The Pr treatment showed no hypocholesterolemic effect but did significant decrease of colonic mucosal cholesterol. The results seems to suggest that a small dose of Pr may reduce the incidence of colon cancers, perhaps being related, at least in part, to modulation of cholesterol synthesis in situ at the colonic mucosa.

Chemoprevention by pravastatin, a 3-hydroxy-3-methylglutaryl-coenzyme A reductase inhibitor, of N-methyl-N-nitrosourea-induced colon carcinogenesis in F344 rats

A potential chemopreventive action of pravastatin (Pr), a 3-hydroxy-3-methylglutaryl-coenzyme A reductase inhibitor, on colon carcinogenesis was evaluated in F344 rats. All rats at 7 weeks of age received an intrarectal dose of 2 mg of N-methyl-N-nitrosourea 3 times weekly for 2 weeks in experiment I (2 groups of 16 rats each), and for 3 weeks in experiment II (4 groups of 30 rats each). They were given drinking water containing 0 ppm (control) or 200 ppm Pr during weeks 1 to 40 in experiment I, and containing 0 ppm (control), 25 ppm, 5 ppm and 1 ppm Pr during weeks 4 to 40 in experiment II. The body weight gains, and food and water intakes were similar in all the groups. The incidence of colon carcinomas at termination of the experiment at week 40 was not different in the 200 ppm Pr and control groups in experiment I (63% vs. 69%), while it was significantly lower in the 25 ppm and 5 ppm groups, but not in the 1 ppm Pr group, compared with the control group in experiment II (50%, 48%, and 77% vs. 80%). This inhibitory effect of Pr against colon carcinogenesis was not related to the cholesterol-lowering effect of this agent. We postulate that Pr inhibits the promotion stage of colon carcinogenesis, perhaps through modulation of cholesterol synthesis in situ in the colonic mucosa, thereby suppressing farnesyl isoprenylation of growth-regulating proteins such as p21 ras.

Suppression of human pancreatic cancer growth in BALB/c nude mice by manumycin, a farnesyl:protein transferase inhibitor

Activating mutations of Ki-ras have been detected in most human pancreatic adenocarcinomas. Since Ras protein requires farnesylation to function, we investigated the effects of manumycin, a potent farnesyl:protein transferase inhibitor, on the growth in nude mice of a human pancreatic cancer cell line, MIA PaCa-2, with a point mutation in the Ki-ras gene. Tumor-bearing mice received intraperitoneal injection of 1 or 5mg/kg manumycin daily for 5 days, or 2 mg/kg manumycin daily for 2 weeks. Growth of inoculated tumors was significantly inhibited by the treatment. The treatment significantly (P<0.05) lowered the numbers of bromodeoxyuridine-incorporating tumor cells. Manumycin did not have apparent hepatotoxicity in vivo. Farnesyl:protein transferase inhibitors could offer a new approach for cancer chemotherapy.